NASA astronauts Eric Boe, from left, Barry "Butch" Wilmore and Suni Williams listen as United Launch Alliance engineer Tom Harper discusses aspects of an RL10 engine during a tour of Aerojet Rocketdyne's facility in West Palm Beach, Florida. The engine will be one of two used for the Centaur upper stage during a United Launch Alliance Atlas V mission to launch Boeing's CST-100 Starliner on a flight test carrying a crew. The engine was test-fired as part of acceptance testing to confirm the engine is ready for flight.

NASA astronauts Barry "Butch" Wilmore, from left, Eric Boe and Suni Williams watch as Aerojet Rocketdyne test team engineers direct the test-firing of an RL10 engine at the company's facility in West Palm Beach, Florida. The engine will be one of two used for the Centaur upper stage during a United Launch Alliance Atlas V mission to launch Boeing's CST-100 Starliner on a flight test carrying a crew. The engine was test-fired as part of acceptance testing to confirm the engine is ready for flight.

NASA astronaut Suni Williams watches as Aerojet Rocketdyne test team engineers direct the test-firing of an RL10 engine at the company's facility in West Palm Beach, Florida. The engine will be one of two used for the Centaur upper stage during a United Launch Alliance Atlas V mission to launch Boeing's CST-100 Starliner on a flight test carrying a crew. The engine was test-fired as part of acceptance testing to confirm the engine is ready for flight.

NASA Commercial Crew astronaut Eric Boe listens as Jim Moss, site director for Aerojet Rocketdyne's West Palm Beach facility, discusses aspects of the RL10 engine as it stands in a vacuum chamber at Aerojet Rocketdyne's test stand in West Palm Beach, Florida. The engine will be one of two used for the Centaur upper stage during a United Launch Alliance Atlas V mission to launch Boeing's CST-100 Starliner on a flight test carrying a crew. The engine was test-fired as part of acceptance testing to confirm the engine is ready for flight.

Carlos Rodriguez, from left, manager of systems development, verification and testing for Aerojet Rocketdyne, talks with NASA astronauts Barry "Butch" Wilmore, Eric Boe and Suni Williams as the group surveys an RL10 engine as it stands in a vacuum chamber at Aerojet Rocketdyne's test stand in West Palm Beach, Florida. The engine will be one of two used for the Centaur upper stage during a United Launch Alliance Atlas V mission to launch Boeing's CST-100 Starliner on a flight test carrying a crew. The engine was test-fired as part of acceptance testing to confirm the engine is ready for flight.

NASA astronaut Eric Boe watches as Aerojet Rocketdyne test team engineers direct the test-firing of an RL10 engine at the company's facility in West Palm Beach, Florida. The engine will be one of two used for the Centaur upper stage during a United Launch Alliance Atlas V mission to launch Boeing's CST-100 Starliner on a flight test carrying a crew. The engine was test-fired as part of acceptance testing to confirm the engine is ready for flight.

NASA astronauts Suni Williams, from left, Eric Boe and Barry "Butch" Wilmore survey an RL10 engine as it stands in a vacuum chamber at Aerojet Rocketdyne's test stand in West Palm Beach, Florida. The engine will be one of two used for the Centaur upper stage during a United Launch Alliance Atlas V mission to launch Boeing's CST-100 Starliner on a flight test carrying a crew. The engine was test-fired as part of acceptance testing to confirm the engine is ready for flight.

NASA astronauts Eric Boe, from left, and Barry "Butch" Wilmore listen as an Aerojet Rocketdyne engineer discusses aspects of an RL10 engine during a tour of Aerojet Rocketdyne's facility in West Palm Beach, Florida. The engine will be one of two used for the Centaur upper stage during a United Launch Alliance Atlas V mission to launch Boeing's CST-100 Starliner on a flight test carrying a crew. The engine was test-fired as part of acceptance testing to confirm the engine is ready for flight.

NASA astronauts Barry "Butch" Wilmore, from left, Eric Boe and Suni Williams survey an RL10 engine as it stands in a vacuum chamber at Aerojet Rocketdyne's test stand in West Palm Beach, Florida. The engine will be one of two used for the Centaur upper stage during a United Launch Alliance Atlas V mission to launch Boeing's CST-100 Starliner on a flight test carrying a crew. The engine was test-fired as part of acceptance testing to confirm the engine is ready for flight.

Carlos Rodriguez, from left, manager of systems development, verification and testing for Aerojet Rocketdyne, talks with NASA astronauts Barry "Butch" Wilmore, Eric Boe and Suni Williams as the group surveys an RL10 engine as it stands in a vacuum chamber at Aerojet Rocketdyne's test stand in West Palm Beach, Florida. The engine will be one of two used for the Centaur upper stage during a United Launch Alliance Atlas V mission to launch Boeing's CST-100 Starliner on a flight test carrying a crew. The engine was test-fired as part of acceptance testing to confirm the engine is ready for flight.

An RL10 engine stands in a vacuum chamber at Aerojet Rocketdyne's test stand in West Palm Beach, Florida. The engine will be one of two used for the Centaur upper stage during a United Launch Alliance Atlas V mission to launch Boeing's CST-100 Starliner on a flight test carrying a crew. The engine was test-fired as part of acceptance testing to confirm the engine is ready for flight.